Variable inductance



June 1, 1948. w K 2,442,373

VARIABLE mnuc'rmcn Filed Nov. 21, 1944 2 Sheets-Sheet 1 INVENTOR.

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June 1, 1948. NEWKlRK 2,442,373

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Prior to the present invention, it has beencommon practice to vary inductance simultaneously with variationof capacity in order to give a wide frequency range. This has been done in various ways. For instance, for low frequencies a variometer and a variable condenser on and operated by the same shaft were common practice. And for high frequencies, a type generally known as the butterfly circuit is widely used. This type comprises a rotor having a plurality of spaced plates adapted to be rotated between the corresponding plates of the stator. Another type for high frequencies is well illustrated by that of General Radio Company, known as the wavemeter as set forth in United States Patents Nos. 1,525,778 and 1,542,995.

The known types of low frequencies were not practically usable for high frequency because both inductance and capacity were too high.

Known types for high frequencies are not thoroughly satisfactory for several reasons. For instance, the butterfly type cannot be loaded so as to deliver sufficient usable power for the greater power requirements, although for very low power requirements, it is thoroughly satisfactory. On the other hand, the type of General amended April 30, 1 928: 870 0- G. 757) Fig. 5 is an enlarged fragmentary cross-section of Fig. 1; and

Fig. 6 is a diagrammatic view showing location of the invention in a well known type of radio high frequency circuit.

Although a variable condenser is not a part of the invention or essential to its operation, it is, under some circumstances, used with the invention. For that reason a well known type of variable condenser has been illustrated as connected to and operating with the invention. It comprises the usual fixed spaced plates, a corresponding number of cooperating rotatable plates and a revoluble shaft carrying and operating the rotatable plates. It is not believed that further description of the condenser is either necessary or desirable as its details are well known to those skilled in the art to which this invention relates.

Referring to the drawings in detail, the variable inductance of this invention comprises two concentric conducting rings l and 2, each provided with an appreciable gap 5 and I, respec- Radio Company above referred to is not suitable produced variable inductance device for high frequency applications.

In order to more clearly disclose the construction, operation and use of the invention, reference should be had to the accompanying drawings forming part of the present application. Throughout the several figures of the drawings, like reference characters designate the same parts in the different views.- In the drawings:

Fig. 1 is a plan view of the invention with the elements in one position; 18:38. 2 is a side elevation'with the parts rotated Fig. 3 is a view showing the rotatable ring at 90 rotation;

Fig. 4 is an enlarged fragmentary cross-section onlinel-l ofFig. 1;

tively, in its circumference. The outer ring i is fixed or stationary, while the inner ring 2 revolves through the outer about a common diameter of the nested rings. The two rings are mounted on an insulating shaft 3 of polystyrene or other acceptable insulating material which extends diametrically across or through the assembled rings. Each ring is a band of appre ciable width, as shown, the dimensions varying according to the particular circumstances of use. They are, too, of approximately the same width.

As shown, they are, substantially, sections of cylinders or cylindrical. the revoluble one having a slightly raised ridge ll circumferentially thereof and midway of its width to better maintain nearness of approach to ring I throughout its rotation therethrough. Preferably, however, they are spherical bands or bands which may be considered as sections of a sphere. Such bands, during rotation of one through the other in accordance with this invention, when of such spherical construction, maintain the original spacing with less variation than is the case where the bands are cylindrical. The outer ring is mounted in free turning'relation on shaft 3 but is held against turning by the connection 4 which is also one of the lead wires or conductors of the inductance. One end of that lead is connected to the free end of the outer ring adjacent the gap 5 therethrough, while the Opposite end of that lead is connected to an adjacent stationary part or member such as the condenser frame. distance between the two connections is short. While this has been found satisfactory, a more rigid connection may be used when desired. This mounting permits shaft 3 to rotate freely in ring The- I. On the other hand, the inner ring 2 is fixed or secured to shaft 3 to rotate therewith. The other lead of the circuit is passed axially through a bore 1' and a communicating, somewhat radially-directed bore 8' in shaft 3 and brought out for connection to the free end of the inner ring 2 adjacent gap 6. The other end of this lead is shown as connected to the condenser shaft to which the shaft 3 may be secured in any usual and well known manner. Where a condenser is not used, as may be frequently the case, this lead, as well as the other one will simply constitute part of any circuit acceptable for the purposes of the invention.

It will be noticed that shaft 3 passes through both rings at a point a short distance from one end thereof, extends diametrically across them and again passes through them at a point diametrically opposite the first point of connection.

For purposes of the present invention, the rings I and 2 should be spaced apart a distance no greater than that sufficient to prevent voltage breakdown. A greater distance would im air the frequency range. In order to maintain this spacing, the outer or free end of shaft 3 is reduced in diameter as at 1, providing a shoulder 8 engaging the inner face of ring 2, thereby limiting inward or separating movement of ring 2 relatively to ring I. On this reduced extension 1 is a conical spacing washer 9, disposed between I and 2. While this washer is of insulating material, it is advisable, at this point, to increase as far as practicable, the length of the electrical leakage path between the two rings to offset possible voltage breakdown along the surface of the washer. To that end, a conical seat 10 is provided in ring I concentric with the bore for shaft 3 but of such pitch or incline that it will be spaced from the corresponding surface of 9 throughout the surface of 9 to the inner end of the seat I0. By such construction, the rings will be maintained spaced but voltage breakdown along the washer surface will be minimized.

The common contact completing the metallic circuit is a conducting washer I2 disposed about shaft 3, diametrically opposite washer 9 and between rings l and 2. Through this washer the current passes direct from one ring to the other. It is the only point at which the current may pass from one ring to the other. It is adjacent the gap in stationary ring I and adjacent gaps 5 and 6 when they are aligned.

With the rings concentrically disposed, the gaps 5 and B being at opposite sides of the shaft 3 or axis of rotatiomthe incoming current, at a given instant, may be considered as entering one ring through one lead, following around that ring in one direction to washer l2, crossing through that to the adjacent end of the other ring and travelling in the same direction through that ring to the other lead, thereby completing the circuit. In that position, the two rings have an additive effect so that inductance is at a maxi- By rotating ring 2 180 degrees, the rings will again be concentrically disposed but with the fundamental difference that gaps 5 and B will be aligned. This disposition compels the current to follow a different path. In this arrangement, the current entering through one lead into one end of one ring, after travelling through it to the washer l2, will pass through washer I2 into the adjacent end of the other ring, but, due to the changed position of the gap 6, will be compelled to reverse the direction of its flow through a 4 the other ring. This produces a cancelling effeet so that inductance is reduced to a minimum.

An arbitrary starting point in operationof the invention could be either of the above 180 degree-separated positions. Rotation from either of those positions toward the other would vary the inductance gradually. The diagrammatic view shows the invention included in a simple oscillator circuit, rings 1 and 2 being indicated. In that diagram the rings are set in the maximum inductance or additive positions. I In the resonant circuits of the hereinabove mentioned wavemeter of the General Radio Company, the cold point or the D. 0. feed point is not stationary and therefore not suitable for use as an oscillator tank. Other resonant circuits of that general type all have the same difficulty or disadvantage. Additionally, all resonant circuits, including both the above wavemeter type and types using an inductance coil in which the number of effective turns may be varied by a mechanical slider or follower have the serious disadvantage of dead end effect. The present invention, having the cold point or D. C. feed point I 3 on ring I close to the shaft 3, provides a cold point or D. C. feed point substantially stationary relative to the complete oscillator circuit, While tuning through the frequency range of the oscillator. By this invention, therefore, both above disadvantages are either eliminated or greatly minimized.

It is thought that the construction, operation, and use of the invention will be clear from the preceding detailed description.

Changes may be made in the construction, arrangement and disposition of the several parts of the invention within the scope of the appended claims without departing from the field of the invention and it is meant to include all such within this application wherein only one preferred form has been illustrated by way of example and with no thought or intention of, in any way or degree, limiting the invention thereby.

Having thus described my invention, what I I claim and desire to protect by Letters Patent is:

-1. A variable inductance for radio high frequency applications comprising two concentrically mounted and spaced conducting rings, one of said rings being revoluble within the other about a common diameter of said rings, said rings being circumferentially interrupted to form a similar gap in each ring, the gap ends of each ring being complementary to those of the other ring when the gaps are in register, conductive means connecting said rings adjacent one pair of the complementary ends, means for rotating the revoluble ring from a concentric position of alignment of the aforesaid gaps to a position degrees removed therefrom andconnections between said rings and the leads of a circuit. 2. A variable inductance for radio high frequency application comprising a conducting ring circumferentlally interrupted to form a gap therein, an insulating rod extending diametrically through said ring and freely revoluble in said ring, a second ring similarly interrupted, mounted on and revoluble with said rod to and from a position concentric within, in the same plane as, spaced from-and with its gap ends aligned with the gap ends of the first mentioned ring, a conductor establishing contact between said rin adjacent the gap end of each ring closest to said rod, means for rotating the revoluble ring to and from a concentric position of alignment of the aforesaid gaps and a position 180 removed therefrom, and connection between said rings and the leads of a circuit.

3. A variable inductance for radio high frequency application comprising a conducting ring circumferentially interrupted to form a gap therein, an insulating rod extending diametrically through said ring and freely revoluble in said ring, a second ring similarly interrupted, mounted on and revoluble with said rod to and from a position concentric within, in the same plane spaced from and with its gap aligned with the gap of the first mentioned ring so that the gap ends of each ring are complementary to those of the other ring, a spacing washer of insulating material disposed about the aforesaid rod between said rings and having an extended leakage attenuating surface, a conductor establishing contact between said rings adjacent a pair ofcompiementary ends of said rings, means for rotating the revoluble ring to and from a concentric position of alignment of the aforesaid gaps and a position 180 removed therefrom and connections between said rings and the leads of a circuit.

4. A variable inductance for radio high frequency application comprising a gapped conducting ring, an insulating rod extending diametrically through said ring and freely revoluble in said ring, a second gapped ring mounted on and revoluble with said rod to and from a position concentric within, in the same plane as, spaced from and with its gap ends aligned with the gap ends of the first mentioned ring, said second ring being provided with a spacing washer receiving seat disposed concentrically of the aforesaid rod in assembled relation, a spacing washer of insulating material disposed about the aforesaid rod, spaced within said seat from said seat throughout the greater surface of said seat and extending from one ring to the other between said rings and having an extended leakage attenuating surface, the aforesaid rod being provided with a shoulder engaging the inner of said rings and maintaining predetermined space relation therebetween, a conductor establishing contact between said rings adjacent the gap ends of said rings closest to said rod, means for rotating the revoluble ring to and from a concentric position of alignment of the aforesaid gaps and a position of 180 removed therefrom and connections between said rings and the leads of a circuit.

5. A variable inductance for radio high frequency application comprising a gapped conducting ring, a rod extending diametrically through saidring and freely revoluble in said ring, said rod being providedwith a longitudinal conduit bore extending inwardly from one end and a communicating lateral passage remote from that end and having formed adjacent its opposite end a ring supporting shoulder, a second gapped ring mounted on and revoluble with said rod to and from a position concentric within, in the same plane as, spaced from and with its sap ends aligned with the gap ends of the first mentioned ring, said second ring being provided with a spacing washer receiving seat disposed concentrically of the aforesaid rod in assembled relation, a spacing washer of insulating material disposed about the aforesaid rod, spaced within said seat from said seat throughout the greater surface of said seat and extending from one ring to the other between said rings and having an extended leakage attenuating surface, said sec 0nd ring being engaged and maintained in position by the aforesaid shoulder, a conductor establishing contact between said rings adjacent the gap ends of said rings closest to the entrance to said longitudinal conduit bore, means for rotating the revoluble ring to and from a concentric position of alignment and a position of 180 removed therefrom, and connections between said rings and the leads of a circuit, one of said leads extending through the aforesaid bore and passage of the aforesaid rod.

6. A variable inductance for radio higl' frequency applications comprising two circumferentially interrupted, coplanar, concentrically mounted and spaced conducting rings, one of said rings being fixed and the other of said rings being revoluble about a common diameter of said rings, conductive means disposed between said rings, a separating insulating washer disposed opposite said conductive means in a seat in one of the facing surfaces of said rings, said seat being flared from its inner end and contacting the surface of said washer only at said inner end whereby. there is provided an increased electrical leakage path between the rings along the surface of the washer.

7. A variable inductance for radio high frequency applications comprising a pair of nested rings, each of said rings being circumferentially interrupted to form a gap therein, diametrically disposed means to support said rings, said rings being so mounted on said support means that the said gaps formed therein are in register and are arcuately displaced from said support means through less than means to rotate the inner one of said rings whereby the gap formed therein may be arcuately displaced through means carried by said support means adjacent said gaps to electrically connect said rings, and means disposed diametrically opposite said electrical connecting means and carried by said support means to insulate said rings from each other, said means comprising a dielectric washer seated in the outer face of said inner ring and laterally spaced therefrom.

8. A variable inductance for radio high frequency applications comprising a pair of nested rings, each of said rings being circumferentially interrupted to form a gap therein, diametrically disposed means to support said rings, said rings being so mounted on said support means that the said gaps formed therein are in register and are arcuately displaced from said support means, means to rotate the inner one of said rings whereby the gap formed therein may be arcuateiy displaced through 180, means carried by said support means to electrically connect said rings, and

means disposed diametrically opposite said electrical connecting means and carried by said support means to insulate said rings from each other,

said means comprising a dielectric washer seated in the outer face of said inner ring and laterally spaced therefrom.

THOMAS A. NEWKIRK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,666,685 Ciough Apr. 17, 1928 1,913,978 Ewen June 13, 1933 2,093,158 Pratt Sept. 14, 1937 2,194,696 Eickemeyer et a1. Mar. 26, 1640 

